Odds are that the tubes installed have thermionic emissions, i.e. the sound you are hearing. Try a different pair and see what happens.
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Jig is correct. Some 6922/6DJ8 tubes are more prone to microphonics than others. If you have some spares to swap, try that. Sometimes the use of tube dampers can help with that. Herbies Audio Labs HAL-O tube dampers are very good at cutting down microphonics.
The high pitched "ringing" you hear from these tubes might be from microphonics being caused by vibrations in the tube.
(1)Yes it's microphonics alright. Using a pencil-eraser, gently (very very gently) tap on the tube envelope to find out which is the offender.
(2)Let's HOPE that the tubes exhibit a thermionic emission behavior; that's normal & is how they all work! Filament heats the cathode which emits electrons past the control-grid toward the collector plate. Without any thermionic emissions you'll get no usable output.
Thanks for the replies. So if it is indeed microphonics, what options do I have to eliminate it. The ringing is pretty annoying. Even when no music is playing and the tube preamp is left on, the ringing will occur sometimes. Am I correct to assume that I will have to switch out my tubes for ones that are not microphonic? Also will Herbe's Hal-O dampers help?
I have had good success with HAL-O's. I also have had good luck when buying new tubes getting the low noise "LN" variety. It may not eliminate it, but it could greatly reduce it. In my previous post, I left out the "in" in front of correct.
Thermionics are what makes the glass bottle work, to make the music go round-n-round
I would like to add to this forum by saying the SP-2B is a zero negative feedback design & as a result it will require specific tubes that are suitable for this design. Best to purchase a matched pair from Musical Design/ John Hillig who has done extensive research & testing on the right tubes for the SP-2B, that will work properly without exhibiting microphonics and the above mentioned problem. This is the best way to go.
Jig is pulling your leg. ALL tubes operate on the principle of "thermionic emissions". Without thermionic emission the cathode would emit no electrons and the tube would just be a pretty piece of glass. The noise you are experiencing is oscillation or "feedback" caused by the physical elements inside the tube being too suseptable to external vibrations. BWT, RCA did not manufacture a 6922; they relabled. If it says "made in germany" odds are it is a Siemens. Holland or USA likely Amperex.
My expirience with the Emotive Audio Sira LE is same. I switch to the Tung Sol 5687 and got some microphonic noise, especially when touching the volume or the preamp. Well, I like the sound of the Tung Sol 5687 better so the "ring" thing doesn't matter to me. When the music plays, that's what's count.
Linkloping. Much like the 6dj8/6922 family of dual triodes ,the 5687 tends to be very prone to microphonics as well. But certainly not all of them, I concurr with your preference to the sound of the tung sol 5687 as it's far and away the best of it's type, particularly the earlier d getter version. That said: out of 11 examples in my stash,I have 4 that are dead quiet and with zero microphonics..... Speedracer,the same can be said for the 6922/6dj8 family when employed in many preamp circuits, and in many cases you need to cherry pick the quiet ones from a bunch of them. When one's preference is for using nos tubes... it can turn out to be a rather expensive crapshoot to be sure. If you "are" contemplating retubing with nos tubes,your odds of success will be far greater by substituting the 6dj8/6922/e88cc for the uprated seimen 188cc or the telefunken 188cc.These tubes, as well as the dutch amperex 7308 are the best sounding of the nos 6dj8 family next to the hideously expensive cca ,they are true low noise 10,000 hour tubes and should last longer than both you and your preamp.They do tend to be pricey though... Another economical alternative is the original nos soviet miltary 6heb or 6hev dual triodes. These are the quietest 6922 types on the planet. They are very linear tubes and have the tightest matched triode sections to boot . Not to be mistaken with the nasty sounding sovtek 6922's currently marketed to the West. These tubes are really well balanced top to bottom,very smooth with great bass punch and a vivid sounding top end void of the glare you hear with the Sovteks. Well worth searching for and typically priced within $10.00 of the Sovteks. Cheers and have a very Merry Christmas and all the best in the New Year.
I'm sorry to disagree on Christmas eve, but Brucegel's suggestion of using Tesla or Sovtek 6922 tubes will at best have you bored stiff with the sound, and at worst selling your preamp for betraying you. It has been my experience that until I rolled around in NOS--so to speak--I had no idea what my tube equipment was capable of doing.
I had a pair of Siemens go bad recently, and was relegated to a pair of Sovtek's for a few days. I turned the amp off until the replacements arrived...get my drift?
All the best,